Effect of anodizing treatment on the very high cycle fatigue behavior of 2A12-T4 aluminum alloy

The effects of chromic acid anodizing (CAA) and sulfuric acid anodizing (SAA) treatments on the very high cycle fatigue behavior of 2A12-T4 aluminum alloy were investigated through ultrasonic fatigue tests. The results showed that CAA and SAA treatments resulted in an appreciable reduction in the fatigue strength and crack initiation from the interface between the anodizing film and substrate, whereas the fatigue crack of substrate specimens initiated from the specimen subsurface over 5 × 108 cycles. The decrease in fatigue strength of the CAA specimens was associated with the residual tensile stress arising from the elastic mismatch between the anodizing film and the substrate. The defects in SAA film, such as segmentation cracks and overgrowth of the anodizing film into the substrate, contributed to the reduction of fatigue strength and multi-crack initiations. The predicted fatigue limit for SAA specimens well agreed with the experimental results.